Occupancy sensor with dimmer feature and night light and method of lighting control using the same

ABSTRACT

System and method are provided where an occupancy sensor with a time delay function designed to dim the lights, for example as a warning, after a first period of time has expired without detecting room occupancy. The lights remain dimmed for a second period of time, and then are turned off after a third period of time has expired without detecting room occupancy. If occupancy is detected during the first period of time, the lights will remain on. If occupancy is detected during the second or third period of time, the lights will be turned on to, for example, previous brightness. A night light can be added to, and/or incorporated in, an occupancy sensor which includes the dimmer feature.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/620,938, filed Feb. 12, 2015,which is a continuation of U.S.patent application Ser. No. 11/529,709, filed Sep. 29, 2006, issued asU.S. Pat. No. 8,970,372 on Mar. 3, 2015, the entire contents of whichare incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to systems and methods forcontrolling room lighting where an occupancy sensor controls roomlighting using standard infrared and/or motion sensor techniques. Moreparticularly, the present invention relates to lighting systems andmethods for controlling lighting in an area based on occupancydetection, and dimming features associated with reducing and/orincreasing the level of lighting in the area such that a warning can beprovided to room occupants when the level of lighting in the room isabout to change based on occupancy detection.

2. Discussion of the Background

Conventional light management system for controlling a load circuitwhere a motion sensor is configured to automatically control the loadcircuit and/or the night light based on detected motion is disclosed in,for example, U.S. Pat. No. 6,888,323 to Null et al., the entiredisclosure of which is hereby incorporated by reference. As described inU.S. Pat. No. 6,888,323 to Null et al., a light management systemincludes a manual wall switch for manually operating a room light. Asshown in FIGS. 2-4 thereof, night light unit provides reduced or lowlevel room lighting when the room light is off. A motion sensor adjustsroom light and/or the night light unit based on a detected occupancy ofthe room. A light sensor unit detects a level of room lighting andadjusting the room light and/or night light unit based on a level ofdetected room lighting. The manual switch, the night light unit, themotion sensor unit and the light sensor unit 205 are integrated tooperate collectively. As shown in a flow chart of FIG. 5, motion in aroom is monitored to determine if a room is occupied, and if the room isnot occupied and the light is not on then the system continues tomonitor for motion in the room. On the other hand, if the room is notoccupied and the room light is on, then the room lighting is lowered orreduced by turning off the room light, dimming the room light, turningthe night light off, dimming the night light or a combination thereof.Alternatively, or in addition to reducing the level of light emittedfrom the room light, the level of light emitted from the night light isalso increased. If the room is occupied, room lighting conditions areassessed by the light sensor, and if the system determines that there isan insufficient level of room lighting, then the level of room lightingis increased by increasing the amount of light that is emitted by theroom light and/or the night light. Alternatively, or in addition toincreasing the level of light emitted from the room light, the level oflight emitted from the night light is also decreased. The level of lightemitted by the night light is integrally associated with the level oflight emitted by the room light such that the night light and the roomlight work together to ensure adequate lighting in the room.

Another conventional device for controlling the level of light in a roomas a function of sensed occupancy and ambient light is disclosed in U.S.Pat. No. 5,406,173 to Mix et al., the entire disclosure of which ishereby incorporated by reference. The device described in U.S. Pat. No.5,406,173 to Mix et al., as shown in FIG. 1 thereof, includes a sensorthat detects whether the room is occupied, a timing circuit that detectsthe duration of time that the room is occupied and unoccupied, a lightmeter that detects the level of ambient light entering the room, andcontrol circuitry that controls the lights in the room in response tothe sensor and light meter. As shown in FIG. 4, this device has threemodes of operation: (1) when the room is occupied, it is determinedwhether the brightness output by lighting unit should be increase ordecreased based on increases or decreases of ambient light detected bylight meter; (2) when the room is unoccupied for a brief period of time,light control circuit 120 freely adjusts the brightness created bylighting unit 150 up and down to compensate for increases or decreasesin the measured ambient light level; and (3) when the room has beenunoccupied for a substantial time period, light control unit turns thelighting unit off to remain off until occupancy detector detects thepresence of a person in the room again sending a signal to the lightcontrol circuit which switches the lighting unit on at the light leveldetermined by light level adjustor.

U.S. Pat. No. 6,275,163 to Bogorad et al., the entire disclosure ofwhich is hereby incorporated by reference, discloses a conventionaloccupancy sensor which is combined with an automatic dimmer to controlthe on/off state of a lamp and its level of brightness. According toU.S. Pat. No. 6,275,163 to Bogorad et al., automatic switch/dimmerincludes an occupancy sensor which provides line output to amicroprocessor logic device, which is connected to a key or a presentcontrol. As shown in FIG. 3 of U.S. Pat. No. 6, 275,163 to Bogorad etal., the output of the microprocessor logic device is fed to a dimmermodule which turns the lamp on or off or can be stepped down frommaximum light output to minimum brightness. According to operationflowchart of FIG. 1 of U.S. Pat. No. 6,275,163 to Bogorad et al., theoperation of its automatic switch/dimmer is described as follows. At thestart of operation, automatic switch/dimmer device is in attentionstate, that is monitoring motion while the lamp is off If no motion isdetected, a signal is generated to command the switch/dimmer to maintainthe present condition. If motion is detected, a signal is generated toturn the lamps on and increase the brightness level towards maximumbrightness. If a the key is not operated, then the lamp goes to maximumbrightness. If a key has been activated, a signal is generated tocontrol the lamp brightening to stop at the key setting, whereby thelamp remains on, and the device returns to the attention state. Ifmotion is detected, a signal is generated to retain the lamp at thelevel selected. This operation will continue as long as motion isdetected. If motion is not detected, a signal is generated to cause thelamp to slowly dim. If no motion is further detected, a signal isgenerated to place the device in its attention state. If motion isdetected, then a signal is generated to cause the lamp to go on to itspreviously selected brightness, and the sensor returns to its attentionstate.

U.S. Pat. No. 5,489,827 to Xia, the entire disclosure of which is herebyincorporated by reference, discloses a system for controlling theintensity of a lamp including a remote sensing device, which is separatefrom the light controller and independent of a utility power line, fordetecting the presence of an occupant within an area. This patentdiscloses the use of a remote dimming controller for remotely adjustingthe illumination level of a light fixture, such that in the absence ofan occupancy signal received from the transmitter within a “second”predetermined period of time (for example, about 12 minutes), thecontroller automatically reduces the level of illumination produced bythe lamp to the lowest non-zero illumination level. When no occupancysignal is received within a “third” predetermined period of time (forexample, about 90 minutes), the light controller controls turning offpower to the lamp.

None of the prior art systems provide any warning, for example topersons who may still occupy the room, that the level of lighting in theroom is about to change based on, for example, the lack of motiondetected by the occupancy sensor.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address at least theabove problems and/or disadvantages and provide at least the advantagesdescribed below. Accordingly, an aspect of the present invention is toprovide a.

Exemplary embodiments of the present invention provide a system andmethod where an occupancy sensor with a time delay function designed todim the lights, for example as a warning, after a first period of timehas expired without detecting room occupancy. The lights remain dimmedfor a second period of time, and then are turned off after a thirdperiod of time has expired without detecting room occupancy. Ifoccupancy is detected during the first period of time, the lights willremain on. If occupancy is detected during the second or third period oftime, the lights will be turned on to, for example, previous brightness.

In an exemplary implementations of certain embodiments of the presentinvention, the first, second and third time periods can be varied and/orpreset, and the light level (brightness) before, after and during thedimming can also be preset and/or varied.

In yet another exemplary implementation, the level of brightness whenthe lights are dimmed, for example during the second time period, isfixed to be approximately one half the level of brightness when thelights were on during, for example, the first time period.

According to other exemplary embodiments of the present invention, anight light can be added to, and/or incorporated in, an occupancy sensorwhich includes the dimmer feature.

In an exemplary implementation of the present invention, the night lightis a light emitting diode (LED) which is positioned behind a passiveinfra red (PIR) lens of an occupancy sensor to illuminate the lens areawhen the lights are off, that is, when the sensor's load is off.

In yet another exemplary implementation of the present invention, theLED can also be mounted through the housing of an occupancy sensor toprovide a more direct light.

LED of any color can be implemented to provide the night light.

In yet another exemplary implementation, a photocell can be added todetect ambient light so that the LED is activated only if there isinsufficient ambient light.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1A shows an operational flowchart of system according to anexemplary embodiment of the present invention.

FIG. 1B shows an operational flowchart of system according to anotherexemplary embodiment of the present invention.

FIGS. 2A-2D show an example of an implementation of an embodiment of thepresent invention as a set of computer executable instructions.

FIG. 3A is a block diagram of a system according to an exemplaryembodiment of the present invention.

FIG. 3B is a block diagram of a system according to another exemplaryembodiment of the present invention.

FIG. 4 is a circuit diagram of a system according to an exemplaryembodiment of the present invention.

FIGS. 5A and 5B illustrate an occupancy sensor according to an exemplaryimplementation of certain embodiments of the present invention.

FIGS. 6A-6D are diagrams of perspective views of an occupancy sensor andindicator LED according to an exemplary implementation of certainembodiments of the present invention.

FIGS. 7A-7D illustrate an occupancy sensor according to anotherexemplary implementation of certain embodiments of the presentinvention.

FIGS. 8A and 8B illustrate an exemplary implementation of a night lightfeature according to certain exemplary embodiments of the presentinvention

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views,embodiments of the present invention are shown in schematic detail.

The matters defined in the description such as a detailed constructionand elements are nothing but the ones provided to assist in acomprehensive understanding of the invention. Accordingly, those ofordinary skill in the art will recognize that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the invention. Also, well-knownfunctions or constructions are omitted for clarity and conciseness.

At the outset, it is noted that exemplary embodiments of the presentinventions are applicable to, and may share certain features with,occupancy sensors disclosed in U.S. Pat. Applications Nos. 6,151,529 and5,699,243, and the entire disclosures of both of these patents arehereby incorporated by reference.

According to exemplary embodiment of the present invention, a system andmethod are provided where an occupancy sensor with a time delay functionis designed to dim the lights, for example as a warning, after a firstperiod of time has expired without detecting room occupancy. The lightsremain dimmed for a second period of time, and then are turned off aftera third period of time has expired without detecting room occupancy. Ifoccupancy is detected during the first period of time, the lights willremain on. If occupancy is detected during the second or third period oftime, the lights will be turned on to, for example, previous brightness.

In an exemplary implementation, once the time delay feature of anoccupancy sensor has reached the end of its cycle, the lights controlledby the switch will dim to a warn the room occupants that the lightingfixtures are about to be turned off. Once motion is detected again bythe device the lighting fixtures controlled by the device will return tofull brightness.

An example of a wall mounted passive infrared occupancy sensor inaccordance with an embodiment of the present invention is illustrates inFIGS. 5A and 5B where an occupancy sensor 500 comprises housing 510,passive infrared (PIR) lens 516 and a front press switch (FPS) 550 whichcan be used to manually switch lights on and off. A dimming control andairgap switch are provided and operated by means of a front mountedslide pot 514 which slides in the housing opening 512 to allowperforming manual dimming function for providing variable outputlighting level. A timer 520 is provided to provide a manually adjustabletime out for sensor 500. An occupancy detection indicator can beprovided by means of an LED 518. FPS 500 can be implemented to have acontoured main body 554 and protruding receptacle 556 that removablyengages cylindrical switch 522. Clips 552 can be provided for additionalstability and engagement with corresponding recesses (shown, but notlabeled) in the front portion of occupancy sensor 500.

In an exemplary implementation, the light level can be continuouslyvariable between 10% and 100% of full brightness. The 10% lighting levelcan be the designed minimum lower limit to prevent wasted power (thatis, the lights set where the lamp's filament will not be visible butpowered).

In an exemplary implementation, the sensor is configured to dim thelight to 50% of current brightness level when a certain preset time (forexample, 60 seconds) a pending before for the lights are switched off towarn occupants that the lights are about to switch off If occupant issensed (for example occupant responds to the warning by a movement), thetime delay is reset back to the original delay set by the time outadjustment (for example, by time out sensor 500 of FIG. 5A).

In an exemplary implementation, a soft start feature is provided wherebya delay (for example, a slight delay) occurs before the lights areturned on to full current brightness. This feature facilitates a lessabrupt transition between different brightness levels, such as from 50%on to 100% on.

In an exemplary implementation of an occupancy sensor according to thepresent invention, any one, or combination, of the following feature canbe implemented:

-   -   Immunity to false tripping—radiated and conducted RFI    -   Zero Cross Switching on both close and open    -   Manual ON switch SW (only way lights turn ON—except during Grace        Time)    -   Auto ON option for turning the lights on automatically anytime        an occupant enters occupancy sensor field of view (FOV). The FPS        works as an on/off override    -   50% dim down for 30 seconds before lights off, for example if        load is at 100% dim to 50%, if load is 50% dim to 25%.    -   Soft start: this feature ramps the light level up or down        anytime it's changed (for example, soft start time=2        seconds)−can be implemented to work for 50% dim down feature    -   standard US Mounting Height: 42″ to 54″    -   North American Box Mounting 120V 60 Hz

Loads: 400-500 Watts Incandescent; Min Load: 40-50 Watts Incandescent;“0” HP required

-   -   Sensor Field of View:        -   1. Operate in a 12×20 Room        -   2. NEMA WD-7 Occupancy Motion Sensors—½ Scale Coverage            Distance; 150 Field of View    -   Light Adjustment:        -   1. Not used in manual on.        -   2. Used in auto on sensors. Daylight set push button to set            calibration, lights off, average readings over 30 sec.            Offset to leave lights off after calibration. Next time            occupant enters read photocell check if ambient>calibrated            level=leave light off, else, if<calibrated level=switch            light on. Photocell is checked˜1×/min. if lights are off.            Lights never switch off while occupant in area based on            photocell.    -   Time Adjustment: Test (30 sec), 10, 20, 30 minutes    -   Line/Load/Ground wires marked (no neutral needed to operate)    -   Green indicator LED flashes when sensing motion    -   Night light    -   FCC Part 15 Subpart B Class A Compliant    -   Metal Strap

Airgap off switch

-   -   IPC Class 2    -   Dimming control: Vertical dial next to “Manual On” switch    -   Dim control range: 10% to 100% light intensity. 10% low-end        limit prevents off or zero dimming mode=energy waste    -   Dim preset on/off control: Dim preset level is controlled by the        dial and switched on/off via Manual On SW. (Light level goes to        whatever level the dial is set too, and is switched on or off        via the Manual On SW)    -   Operating Temp. Range: 0 C to 50 C        -   Storage Temp. Range: −10 C to +85 C        -   Relative Humidity Range: 20% to 90% non condensing        -   Withstand cold (−18 C) drop test from 3 feet from all axis            in box on a hardwood floor        -   Voltage range performance: −10% to +10%        -   Electrostatic Discharge (ESD) protected        -   Fast transient burst/surge        -   Safe short circuit protection—Line to Neutral or lamp            failure

FIGS. 6A and 6B show schematics of a front and side view of a frontpanel 610 of an occupancy sensor according to an exemplary embodiment ofthe present invention. As shown in FIGS. 6A and 6B, PIR lens 516 ismounded in portions 612 of the front panel, LED indicator 616 is mountedthrough the opening 618 of the front panel (FIGS. 6C and 6D), and body620 of FPS 600 includes a gap 622 foe accommodating a slide pot (seeFIG. 5A) therethrough.

An example of a wall mounted passive infrared occupancy sensor inaccordance with another embodiment of the present invention isillustrates in FIGS. 7A through 7D where an occupancy sensor compriseshousing 710 and front panel 712 secured to housing 710 by means of, forexample, screws 714. Passive infrared (PIR) lens 718 is mounted in part716, which also includes a front press switch (FPS) 722. In contrast toan embodiment illustrated in FIGS. 5A and 5B. manual dimming control isomitted. An occupancy detection indicator can be provided by means of anLED 720.

According to another exemplary embodiment of the present invention, anight light feature can be provided in occupancy sensors describedabove. An exemplary implementation of a night light is illustrated inFIGS. 8A and 8B where night light 800 is positioned with housing 812 ofa PIR (not shown) and behind the PIR lens (not shown). Opening 810 forthe PIR is provide in housing 812. This exemplary implementationprovides LED 814 which can function as a night light (or as anindicator, as described for example in U.S. Pat. No. 5,669,243) and canbe removably secured though an opening in a aside of housing 812 bymeans of a mounting platform 818 and a clip 816. The LED can beconfigured to illuminate the lens area any time the sensor's load isoff. In an exemplary implementation, LED can be selected to operate onlyif there is insufficient ambient light by use of, for example, photocellcontrol. LED light can emit any suitable color of light, for example,white, amber, green, red, and so on. In yet another exemplaryimplementation, LED night light can be mounted through the housing toproduce a more direct/brighter light.

Exemplary implementations of a system and method incorporating a warningdimming function according to certain embodiment of the presentinvention are as follows.

Referring to FIGS. 1A and 1B, after initial power on 100, systeminitialization and warm up 102 take place, after which stand-by mode 104is maintained until a manual operating switch, for example a front pressswitch (FPS) has been pressed down. If it is determined 106 that FPS hasbeen pressed down, values of the voltage regulators (for example,variable resistors) VR of the dimmer and timer circuits (see circuitdiagram of FIG. 4) are read 108, ZC interrupt enable is set 110, and asoft start enabled is set 112, provided for example is a TRIode forAlternating Current (TRIAC). If soft start count is not over, dimcontrol output is performed 116. After the soft start count is over,values of dimmer VR and timer VR are read 118, PIR timer is set andcounts up, and the TRIAC is on 120. PIR signal output is detected 122.On de-bounce “OK”, the operation is returned to step 118, otherwise adetermination is made whether FPS is pressed down 128. If FPS is presseddown 128 , the TRIAC is set to off 132 and operation return back tostandby 104. Otherwise, PIR timer overflow is checked 130 before settingTRIAC to off 132. If PIR timer overflow is confirmed then adetermination is made on the change of dimmer VR and timer VR 126. Ifchange has occurred, operation returns to step 118, otherwise operationreturns to step 122.

In an exemplary implantation of FIG. 1B, steps for tuning on and turningoff nightlight are added whereby the night light is set to off afterstep 134 and set to on after step 132.

Referring to FIGS. 2A through 2D, an exemplary implementation of themethods described in, for example, FIG. 1A in a software program areillustrated by means of logic flow charts 200, 210, 220 and 230 whichcan be programmed for example in an ASIC.

Referring to FIGS. 3A and 3B, block diagrams of systems according toexemplary embodiments of the present invention are provided where anoccupancy sensor comprises a controller 126 having coupled thereto: anamplifier 114 which receives signals from PIR detector 112 coupled tomotion sensor 110; voltage regulator 116; zero crossing circuit 118;time adjustment circuit 120; FPS manual on switch 122; dimmingcontroller 124; oscillator 132; LED driver 128 for driving LED 130; andTRAC driver 134 connected to load 138 via an airgap off switch 136.

In an exemplary embodiment of FIG. 3A, a night light driver 140 fordriving nightlight 142 are also coupled to controller 126.

FIG. 4 is an example of a circuit design implementing the featuresillustrated in block diagrams of FIGS. 3A and 3B as described above withreference to FIGS. 1A and 1B, including night light circuitry 414, LEDindicator circuitry 420; timer circuitry 422; TRIAC driver circuitry412; and a controller implemented by means of a programmablemicroprocessor 400.

Numerous additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

I claim:
 1. A light control system comprising: a sensor for detecting anoccupancy in an area; a timer for determining if the occupancy is notdetected by the occupancy sensor before a first time period expires; adimmer for changing a light level in said area from a first light levelto a second light level when determining that a second time period afterthe occupancy is not detected is remaining on the timer before the firsttime period expires, and for changing said light level in said area fromthe second light level to a third light level when determining that thefirst time period expired and the occupancy is not detected during thesecond time period; and a controller coupled to the sensor, the timerand the dimmer to control the light level to remain at the second lightlevel until the first time period expires if the occupancy sensor doesnot detect occupancy during the second time period, change to the firstlight level from the second light level, and reset the timer to thefirst time period, if the occupancy sensor detects occupancy during thesecond time period, and change to a third light level from the secondlight level, when the first time period expires if the occupancy sensordoes not detect occupancy during the second time period; wherein: thesecond light level is lower than the first light level; and the thirdlight level is lower than the first light level.
 2. The light controlsystem of claim 1, wherein at least one of the first and second timeperiods comprises at least one of a variable and preset time period. 3.The light control system of claim 1, wherein at least one of the first,second and third light levels comprises at least one of a variable andpreset level.
 4. The light control system of claim 1, further comprisinga night light.
 5. The light control system of claim 4, wherein the nightlight comprises a light emitting diode (LED).
 6. The light controlsystem of claim 4, wherein the night light is configure to be on whenthe lights source is off and to be off when the light source is on. 7.The light control system of claim 4, further comprising a photocellconfigured to detect ambient light whereby at least the first lightlevel is adjusted based on the detected ambient light.
 8. A method ofcontrolling light output, the method comprising: detecting an occupancyin an area; determining if the occupancy is not detected in the areabefore a first time period expires on a timer; determining if a secondtime period after the occupancy is not detected is remaining on thetimer before the first time period expires; changing a light level insaid area from a first light level to a second light level whendetermining that the second time period after the occupancy is notdetected is remaining on the timer before the first time period expires;controlling the light level to remain at the second light level untilthe first time period expires if the occupancy sensor does not detectoccupancy during the second time period; changing the light level to thefirst light level from the second light level, and resetting the timerto the first time period, if the occupancy sensor detects occupancyduring the second time period; and changing the light level to a thirdlight level from the second light level, when the first time periodexpires if the occupancy sensor does not detect occupancy during thesecond time period, wherein second light level is lower than the firstlight level, and the third light level is lower than the first lightlevel.
 9. The method of claim 8, further comprising: turning on a nightlight if a light source is off; and turning off the night light if thelight source is on.
 10. A non-transitory computer readable medium forstoring thereon a set of computer executable instructions comprising: afirst set of instruction for detecting an occupancy in an area; a secondset of instructions for determining if the occupancy is not detected inthe area before a first time period expires on a timer; a third set ofinstructions for determining if a second time period after the occupancyis not detected is remaining on the timer before the first time periodexpires; a fourth set of instruction for changing a light level in saidarea from a first light level to a second light level when determiningthat the second time period after the occupancy is not detected isremaining before the first time period expires; a fifth set ofinstruction for controlling the light level to remain at the secondlight level until the first time period expires if the occupancy sensordoes not detect occupancy during the second time period; sixth set ofinstruction for changing the light level to the first light level fromthe second light level, and resetting the timer to the first timeperiod, if the occupancy sensor detects occupancy during the second timeperiod; and a seventh set of instructions for changing the light levelto a third light level from the second light level, when the first timeperiod expires if the occupancy sensor does not detect occupancy duringthe second time period, wherein the second light level is lower than thefirst light level, and the third light level is lower than the firstlight level.
 11. The light control system of claim 1, further comprisinga light source connected to the dimmer and outputting light at the lightlevel wherein if the occupancy sensor detects occupancy during thesecond time period, the controller controls the light level to graduallychange from the second light level to the first light level over afourth time period wherein the changing to the first light level if theoccupancy sensor detects occupancy during the second time periodcomprises gradual change to the first light level from the second lightlevel over a fourth time period.
 12. The method of claim 8, wherein atleast one of the first and second time periods comprises at least one ofa variable and preset time period.
 13. The method of claim 8, wherein atleast one of the first, second and third light levels comprises at leastone of a variable and preset level.
 14. The method of claim 9, whereinthe night light comprises a light emitting diode (LED).
 15. The methodof claim 8, further comprising: detecting ambient light; and adjustingat least the first light level based on the detected ambient light. 16.The method of claim 8, further comprising configuring a light source tooutput light at the light level, wherein the changing the light level tothe first light level if the occupancy sensor detects occupancy duringthe second time period comprises gradually changing the output lightfrom the second light level to the first light level over a fourth timeperiod.